Adsorption rate of CO2 and water on molecular sieves
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Which is faster, the adsorption rate of CO2 or that of water on molecular sieves?
I think the first thing to consider is which type of molecular sieve to use. For example, 13X likely does not absorb water as quickly as alumina; after all, it is alumina that absorbs water primarily, while molecular sieves are responsible for adsorbing carbon dioxide
If natural gas contains 9% CO2 and 500 PPM water, which will be adsorbed completely first when using molecular sieves?
Molecular sieves adsorb water at a faster rate than carbon dioxide. Regarding the issue on the 3rd floor, water is absorbed completely first, followed by carbon dioxide; once water has been absorbed, it is not easy to desorb it
Excuse me, those upstairs: if the molecular sieve being used has already absorbed CO2 and water, can raising the temperature during desorption help to completely remove CO2 and water? Also, if one only wants to adsorb one of these substances, which type of molecular sieve would be suitable?
It’s obviously water; molecular sieves are hydrophilic and absorb water first. Or considering the volume of the molecules, the H2O molecules are smaller than those of CO2; therefore, H2O is adsorbed first. The molecular sieve used in our unit is of type 13X. The feed gas contains 500 ppm of H2O, 20 ppm of CO2, and 100 ppm of CH3OH. After passing through the molecular sieve, analysis showed that no water or methanol was detected, while the CO2 concentration was around 0.5 ppm.
Let’s see how the regeneration is going – we’re using 13X
Regardless of the type of molecular sieve, it adsorbs water first. Water has a high degree of polarity. Regeneration is not easy; heating and evacuation are required for better regeneration, but severe pulverization occurs. There are more benefits to carbon dioxide.
1. Heating can enable the simultaneous removal of CO2 and H2O from molecular sieves. 2. If only dehydration is carried out without CO2 removal, then only 3A molecular sieve 3 can be used. If only CO2 is to be removed without removing water, no type of molecular sieve can do anything about it. You need to use other chemical methods to remove CO2. 4. Special treatment for 3: First, use 3A to dehydrate the mixture only, reducing the water content in the gas to a few PPM. In the second step, 5A or 13X is used to remove CO2; the CO2 released through desorption can also be utilized as a by-product.
It’s obviously water; in terms of absorption capacity, its water-absorbing capacity is much greater than that of CO2
I learned a lesson, thank you all!
In air separation, molecular sieves are generally used to remove water first and then carbon dioxide; therefore, alumina is now added below the molecular sieves to remove water first.
13X molecular sieves absorb water much faster than carbon dioxide, but the amount absorbed is not large; therefore, a layer of aluminum oxide is usually placed first to absorb water, followed by the molecular sieves to absorb carbon dioxide. Prevent carbon dioxide from penetrating after the molecular sieve absorbs too much moisture.
There’s a lot to learn and remember for PSA; keep learning* Chinese: loveliness:
Which molecular sieve is more suitable for simultaneously removing trace amounts of water and CO2?
16th floor, what gas do you use?
How is the adsorption capacity of molecular sieves determined? What is the adsorption capacity?
I think both can be adsorbed; it’s just that carbon dioxide has a stronger desorption capacity while water has a weaker one, plus water is highly polar!
4A molecular sieve is more suitable. Why is 5A mentioned? All molecular sieves are used for dehydration. 3A only removes water but not carbon dioxide. 4A removes both water and carbon dioxide. 5A not only removes water and carbon dioxide but also H2S from natural gas; however, its price is higher than that of 4A. 13X removes water, carbon dioxide, H2S, and COS as well, and its price is also higher than that of 4A.
Molecular sieves have an extremely strong adsorption capacity for water, followed by acetylene and carbon dioxide； Its adsorption capacity for carbon dioxide and acetylene decreases after absorbing water.